Currently, a non-aqueous electrolyte secondary battery including a lithium ion secondary battery that is utilized for a mobile device such as a mobile phone is available as a commercial product. The non-aqueous electrolyte secondary battery generally has a configuration in which a positive electrode having a positive electrode active material or the like applied to a current collector and a negative electrode having a negative electrode active material or the like applied to a current collector are connected to each other via an electrolyte layer in which a non-aqueous electrolyte solution or a non-aqueous electrolyte gel is held in a separator. Further, charge and discharge reactions of a battery occur as ions such as lithium ions are absorbed into and desorbed from an electrode active material.
Incidentally, in recent years, it has been desired to reduce the amount of carbon dioxide in order to cope with global warming. Hence, a non-aqueous electrolyte secondary battery having a small environmental burden has been used not only in a mobile device or the like but also in a power source device of an electrically driven vehicle such as a hybrid vehicle (HEV), an electric vehicle (EV), or a fuel cell vehicle.
A non-aqueous electrolyte secondary battery directed to the application to electrically driven vehicles is desired to have a high output and a high capacity. Further, the non-aqueous electrolyte secondary battery directed to the application to electrically driven vehicles is desired to have cycle characteristics that the capacity can be maintained even when the charge and discharge cycle is repeated for a long period of time.
However, with an increase in capacity of the battery, the density of the negative electrode active material layer increases, and permeation of the electrolyte solution into the negative electrode active material layer is inhibited by the porosity of the negative electrode active material layer decreasing. Thus, the exchange of lithium ions becomes partially difficult, and reaction in the negative electrode active material layer becomes non-uniform in some cases. Due to such a local reaction, a part of the negative electrode active material is in an overcharge or overdischarge state, lithium dendrites occur and reductive degradation of the electrolyte solution easily proceeds, so that cycle characteristics deteriorate in some cases.
JP 2013-179101 A discloses a technique in which composite graphite particles obtained by compositing natural graphite and a carbonaceous substance or a graphitic substance are used as a negative electrode active material of a non-aqueous electrolyte secondary battery. With such a configuration, even when the density of the negative electrode active material layer is increased in order to increase the capacity, a battery in which permeability of the electrolyte solution is favorable and cycle characteristics are excellent can be obtained.